During the course of drilling an oil or gas well, one operation which is often performed is to lower a testing string into the well to test the production capabilities of a hydrocarbon producing underground formation intersected by the well. This test is accomplished by a lowering a string of pipe, commonly referred to as the drill pipe, into the well, with the formation tester valve attached. Another typical tool run into the well is known as a Tubing String Testing Valve (TST), which is a full opening test valve that allows the drill stem test string to be pressure tested while running in the hole. It is desirable prior to conducting a drill stem test, to be able to pressure test the string of drill pipe periodically to determine whether there is any leakage at the joints between successive stands of pipe. To accomplish this drill pipe pressure testing, the pipe string is filled with a fluid and the lowering of the pipe is periodically stopped. When the lowering of the pipe is stopped, the fluid in the string of the drill pipe is pressurized to determine whether there are any leaks in the drill pipe above the TST valve.
In the past, a number of devices have been used to test the pressure integrity of pipe strings. In some instances, pressure is applied against a closed formation tester valve included in the string. In other instances, a tubing tester valve is employed in the string near the packer, and pressure is applied against the valve element in the tubing tester valve.
It is necessary to fill the tubing or drill pipe string with an incompressible fluid as the string is run into the well bore before applying pressure to the interior of the string. In the past, tubing tester valves, when used in a string without a closed formation tester valve therebetween, relied upon the upward biasing of a flapper valve element to allow the test sting to fill with fluid. The flapper valve is biased against a spring by hydrostatic pressure below the tubing tester valve in the test string to gradually fill the test string from below, generally drilling "mud." In other instances, the test string is filled from the top on the rig floor with diesel oil or other fluids. Such a procedure, however, is time consuming and hazardous. Still other tubing tester valves incorporate a closeable bypass port below the valve element so that, even with a closed formation tester valve below, well fluids in the annulus surrounding the test string can enter the vicinity of the tubing tester valve and bias a valve element therein to an open position through hydrostatic pressure, thereby filling the drill string.
At some point during the well service operation, be it cementing, treating, or testing, it is necessary to be able to open the tubing tester valve so that flow from the rig floor down into the formation, which would normally close the valve, may be affected. Tubing tester valves accommodate this necessity in several ways. Some valves provide an opening of the tubing tester valve through a reciprocating and/or rotating the pipe string. Other valves provide for the opening of the valve through a valve actuator operated responsive to an increase in annular pressure.
Once the test string is run to its desired depth, it is necessary to sting, via a set of seals located on the bottom of the test string, into a production packer. If it is necessary, however, to pull the test string up, the TST flapper valve will act as a check valve, thereby causing a pressure decrease due to an increase in volume in the annulus below the TST flapper valve. This decrease in pressure can operate to damage the seals on the bottom of the test string, as well as operate the TST valve itself.
If one of the other tester valves located in the test string have been closed for testing reasons, the pulling in and out of the seals can actually destroy the seal integrity on the stinger of the test string as well as affecting the test string in the production packer, by causing a piston effect due to the closed annulus area.
In the past, bypass valves were not commonly used with TST valves. In the cases where bypass valves are used in conjunction with TST valves, two separate tools must be used.
Therefore, a need has arisen for a well tool apparatus that is capable of supporting a tubing pressure test thereabove, while avoiding damage to production valves and trash build-up in the pressure test valve, and that is capable of allowing the tubing string to sting into and out of production packers avoiding damage to the seal assembly and premature operation of the pressure test valve.